Sludge treatment and reuse as soil conditioner for small rural communities

An alternative method for on-site treatment of sewage sludge for small-scale wastewater treatment installations was developed. Primary Domestic Sludge (PDS) at 40 g dry matter per liter of suspension was supplemented with 10 g of the super-absorbent (SA). The mixture obtained in a matter of minutes was of crumbly consistency without leakage of free water. These crumbs were spread on cardboard supported by an undulated plate. After air drying for 1–2 weeks, depending on the ambient air temperature and humidity, the water content of the crumbs decreased from 96% to 8.5%. The dried residue was used to treat a new volume of primary domestic sludge. This cycle was repeated for more than 15 times and the SA remained active. The technical skills and the costs related to convert PDS to an air-dry residue by means of this SA-based process, appear appropriate for a family or a small community. The final product of the sludge treatment process contained about 50% (w/w) organic material in a stabilised form. It was rich in N and P and it had a high hygienic quality. Greenhouse tests growing maize showed that this final product had soil improving properties.